Carrier 024-036, Service Manual, Page: 22 / 41

: Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
22
lubrication. If bleed hole is plugged, accumulator must be changed. The
accumulator has a fusible element located in the bottom end bell. (See
Fig. 22 .) This fusible element will melt at 430_F/221_C and vent the
refrigerant if this temperature is reached either internal or external to the
system. If fuse melts, the accumulator must be replaced.
To change accumulator:
1. Shut off all power to unit.
2. Recover all refrigerant from system.
3. Break vacuum with dry nitrogen. Do not exceed 5 psig.
NOTE: Refer to appropriate sections of Service Manual for instructions.
A10188
Fig. 21 – Reversing Valve (Heating Mode, Solenoid De-Energized)
4. Remove accumulator from system with tubing cutter.
5. Tape ends of open tubing.
6. Scratch matching marks on tubing studs and old accumulator.
Scratch matching marks on new accumulator. Unbraze stubs from
old accumulator and braze into new accumulator.
7. Thoroughly rinse any flux residue from joints and paint with
corrosion-resistant coating such as zinc-rich paint.
8. Install factory authorized accumulator into system with copper slip
couplings.
9. Evacuate and charge system.
Pour and measure oil quantity (if any) from old accumulator. If more
than 20 percent of oil charge is trapped in accumulator, add new POE or
PVE oil to compressor to make up for this loss. (See Table 3 .)
A88410
Fig. 22 – Accumulator
Thermostatic Expansion Valve (TXV)
The five ton air conditioning and heat pump units have a factory
installed thermostatic expansion valve (TXV). The TXV will be a
bi-flow, hard-shutoff with an external equalizer and a balance port pin.
A hard shut-off TXV does not have a bleed port. Therefore, minimal
equalization takes place after shutdown. TXVs are specifically designed
to operate with R-410A refrigerant, use only factory authorized TXV’s.
Do not interchange R-410A and R-22 TXVs.
TXV Operation
The TXV is a metering device that is used in air conditioning and heat
pump systems to adjust to changing load conditions by maintaining a
preset superheat temperature at the outlet of the evaporator coil. The
volume of refrigerant metered through the valve seat is dependent upon
the following:
1. Superheat temperature is sensed by cap tube sensing bulb on
suction tube at outlet of evaporator coil. This temperature is
converted into pressure by refrigerant in the bulb pushing
downward on the diaphragm which opens the valve via the
pushrods.
2. The suction pressure at the outlet of the evaporator coil is
transferred via the external equalizer tube to the underside of the
diaphragm. This is needed to account for the indoor coil pressure
drop. Coils typically have a high pressure drop, which requires this
valve feature.
3. The pin is spring loaded, which exerts pressure on the underside of
the diaphragm. Therefore, the bulb pressure works against the
spring pressure and evaporator suction pressure to open the valve.
If the load increases, the temperature increases at the bulb, which
increases the pressure on the top side of the diaphragm. This opens
the valve and increases the flow of refrigerant. The increased
refrigerant flow causes the leaving evaporator temperature to
decrease. This lowers the pressure on the diaphragm and closes the
pin. The refrigerant flow is effectively stabilized to the load demand
with negligible change in superheat.
CAUTION
!
PERSONAL INJURY HAZARD
Failure to follow this caution may result in personal injury.
Wear safety glasses, protective clothing, and gloves when handling
refrigerant.
TO INDOOR COIL
TO
ACCUMULATOR
INSULATE
FOR
ACCURATE
READING
FROM
OUTDOOR
COIL
TP-4 TP-3
TP-2
TP-1
INSULATE FOR
ACCURATE
READING
FROM COMPRESSOR
DISCHARGE LINE
ELECTRONIC
THERMOMETER
430
°
FUSE
ELEMENT
A88410